Hybrid buses

Oil prices have climbed to an all-time high; at the same time there is the issue of eco-friendly and low-CO2 freight and passenger haulage high up on the political and social agenda of many countries.
These rising economic and ecological challenges are being addressed by Vossloh Kiepe GmbH with the development of production-stage hybrid technologies for public urban transportation.
Embedded in these technologies is the accumulated expertise derived from a host of successful developments and the production of electric drive systems for vehicles operating on such services.

Energy savings of up to 30 percent

The hybrid drive for city buses, ready for standard production, takes into account the special operating conditions of such vehicles such as lengthy operating periods and repeated stops/start-ups. Achieved is a maximum reduction in fuel consumption and hence exhaust emissions. Measurements have shown that the energy consumption of vehicles powered by this new hybrid technology is up to 35 percent lower compared with conventional diesel engine buses. At the same time, there is none of the typical noise when the diesel engine revs up. The innovation developed by Vossloh Kiepe engineers thus plays an important role in making city traffic greener and quieter.

The basis for this reduction in fuel consumption is an adaptive, smart energy management system. Depending on operating conditions but at a consistent rate, a diesel engine drives a generator while the vehicle is travelling, which in turn is connected via an electric intermediate circuit to the traction motor. When the vehicle is braking, the released energy is absorbed quickly and effectively by the Energy Storage System (ESS) developed by Vossloh Kiepe, and made available for the next acceleration phase. ESS works on the basis of durable, highly dynamic double-layer capacitors (“supercaps”) with a high degree of efficiency. The "supercaps" used in Vossloh Kiepe's ESS can optionally be extended with galvanic batteries.

The Energy Manager, another development from Vossloh Kiepe, controls the flow of energy between the generator, ESS, and traction motor. Thanks to the ample current-carrying capacity (ampacity) of the inverter it is possible to achieve an efficient degree of energy recovery (power feedback). Depending on the type of vehicle and its configuration, operating options can be selected that allow a reduction in diesel engine RPM down to complete shutoff in a variety of time-frames. For instance, the vehicle can start up and brake with the diesel engine switched off, in other words zero emissions and zero noise. Included in the system are functions for actuating ABS, TCS and the trouble-shooting device.

Production-ready hybrid drive for city buses already in use

The modular hybrid propulsion system can be used on single buses with single-axle drive and articulated or multi-articulated buses with dual-axle drive. This is already the case with the 24-meter double-articulated hybrid bus, the "LighTram" developed together with Carrosserie HESS and on show at InnoTrans 2008.
This is a vehicle that closes the gap between bus and tram. With a capacity of up to 251 passengers, it holds a world record for road vehicles. Thanks to its ingenious geometry, the "LighTram" has a tighter turning circle than today’s 18.75-meter articulated buses. With the aid of Vossloh Kiepe’s electric dual-axle drive, it is more quickly off the mark than other diesel buses or trams, thus more speedily threading its way into the flow of traffic.

Maximizing energy efficiency on trolleybuses, too

Among public urban transportation vehicles, trolleybuses have the lowest energy consumption. With its hybrid traction system, ready for series production and specially developed for trolleybuses, Vossloh Kiepe proves that these vehicles can operate even more efficiently.

On the traction system in this case, the engineers at Vossloh Kiepe in Düsseldorf have again combined the conventional traction system of a trolleybus with “supercaps.” These high-performance capacitors are the sole energy storage system able to make available at short notice all of the energy needed for acceleration.
Disconnected from the overhead lines, the trolleybus can drive for up to 400 meters with the energy stored in the "supercaps" in order, for example, to circumvent construction sites.

It is also on dual-mode buses for services which only partly have overhead power lines that the "green" advantages of hybrid technology become manifest. Instead of the 200-kW engine normally used on diesel and conventional dual-mode buses, this system operates on a 100-kW diesel engine for the same running performance, and draws a further 100 kW from the energy storage system.

The drive system from Vossloh Kiepe can be used on small trolleybuses. Also on larger types of vehicles such as double-articulated trolleybuses the system will operate along underpowered sections of the route with no compromise in performance. Starting from 2009, this hybrid traction system will be contributing toward cleaner air in the Italian city of Milan.